Kenji Ohkubo

Thermal conductivity of B2-type aluminides and titanides

Thermal conductivity measurement by the laser-flash method adopted here is very suitable for intermetallic compounds, some of which are too brittle for preparing samples with good geometry. Thermal conductivity data at room temperature are presented in the series of aluminides, FeAl, CoAl and NiAl, titanides, FeTi, CoTi and NiTi, and gallides CoGa and NiGa, in order to reveal the role of 8A group elements of the first transition metal series. Thermal conductivity reaches a maximum at stoichiometry and decreases with deviations from stoichiometry on either side in most of these compounds. The largest thermal conductivities observed are 92 W m−1 K−1 of NiAl among the aluminides, 23 of NiGa among the gallides and 73 of FeTi among the titanides. It is discussed that the thermal conductivity is further reduced as the position of the partner components becomes distant from that of a host component.

Thermal conductivity in Pt-based alloys

Abstract Thermal conductivity of Pt alloys with an fcc single phase was comprehensively surveyed by employing the laser flash method. Thermal conductivity is dominantly determined by alloy composition and temperature and is scarcely influenced by fabrication condition. An addition of solute definitely decreases the thermal conductivity of Pt, and the conductivity-composition relationship is characterized by a sharp maximum at pure Pt. The Wiedemann-Franz relation held for Pt alloys suggests the dominant carrier of thermal conduction is an electron. An empirical rule is proposed that the thermal conductivity decreases significantly as the position of the solute element in the periodic table becomes horizontally more distant from that of Pt. Thermal conductivity of Pt alloys increases with increasing temperature in a range between 300–1100 K, and the temperature coefficient is found to be inversely correlated with the thermal conductivity.

Effects of ternary additions on thermal conductivity of NiAl

Ternary addition generally degrades an excellent conduction properties of NiAl. The contour map of thermal conductivity in NiAl–X β single phase field is drawn for the ternary elements X=Ti, Cu and Ge. It is revealed that each element has a characteristic ridge direction in the contour map. This feature is discussed based on the preference substitutional site of a ternary element, and eighteen ternary elements with a sufficient solubility into NiAl are classified into three groups according to the ridge direction. Thermal conductivity of NiAl-based alloys increases with increasing temperature, however the ridge direction in the contour map remains unchanged.

Thermal conductivity in nickel solid solutions

Thermal conductivity in nickel solid solutions with a γ single phase was comprehensively surveyed. The major findings are summarized as follows: First, alloying definitely decreases the thermal conductivity of nickel. The relationship between thermal conductivity and concentration in the dilute solid solution is characterized by the Nordheim relation. Second, for most solutes, the thermal conductivity of nickel alloys decreases significantly as the position of the solute element becomes horizontally more distant from nickel in the periodic table, which is equivalent to the Norbury–Linde rule of electrical resistivity. Third, cold deformation has no significant influence on the thermal conductivity of nickel alloys. Fourth, a monotonic increase in thermal conductivity as a function of temperature is observed in highly concentrated nickel alloys, while the thermal conductivity of dilute nickel alloys shows a minimum at the Curie temperature.

Thermal conductivity and thermal expansion of L12 intermetallic compounds based on rhodium

Abstract Thermal conductivity and thermal expansion were measured for the L1 2 intermetallic compounds Rh 3 X (X=Ti, Zr, Hf, V, Nb, Ta) in the temperature range between 300 and 1100 K to evaluate the feasibility of applying the compounds to high temperature structural materials. The thermal conductivities of Rh 3 X are widely distributed in the range from 32 to 103 W m −1 K −1 at 300 K, while the difference of the thermal conductivities becomes less emphasized at higher temperatures. A trend is observed that the thermal conductivity of Rh 3 X is larger when the constituent X belongs to group 5 rather than 4 in the periodic table. The coefficients of thermal expansion (CTE) of Rh 3 X slightly increase with increasing temperature, and they are concentrated around 10×10 −6 K −1 at 800 K. A trend is that the CTE of Rh 3 X is reduced as the position of X goes downward in the periodic table. It is demonstrated that Rh 3 Nb and Rh 3 Ta are suitable for high temperature structural applications due to the larger thermal conductivities and the smaller CTE.

Site preference in NiAl—determination by thermal conductivity measurement

Abstract A contour map of thermal conductivity in a ternary intermetallic phase characterizes the direction of the contour ridge, and the ridge direction has been demonstrated to be a reliable indication of site preference of ternary elements in an intermetallic compound. Site preferences of fifteen kinds of ternary elements in NiAl are determined from the ridge direction of thermal conductivity contours in ternary β phase. It is found that V, Nb, Ta, Mo, Fe, Ru, Co and Pt substitute preferentially for nickel, while Ti, Mn, Ga, Si and Ge for aluminum, and Cr and Cu occupy both nickel and aluminum sites.

Thermal conductivity in A3B intermetallic compounds based on iron and nickel

Thermal conductivity of A 3 B intermetallic compounds, where A denotes iron or nickel and B denotes group IIIb or IVb elements, is investigated by a laser-flash method. Among six kinds of L1 2 compounds, the largest thermal conductivity observed is 32 8 Wm −1 K −1 of Ni 3 Ga. In Fe 3 Ga and Fe 3 Ge, three polymorphs, i.e. L1 2 , D0 19 and D0 3 , can be achieved by performing a suitable heat treatment. Thermal conductivity of the D0 19 phase is quite close to that of the L1 2 phase, while the DO, phase shows smaller values. In most A 3 B compounds, the measured thermal conductivities tend to decrease as the position of constituent B becomes horizontally more distant from that of constituent A in the periodic table.

Thermal conductivity of Ni3Al with ternary additions

Abstract The direction of ridge of thermal conductivity contours in a ternary γ′-Ni 3 Al phase agrees with that of solubility lobe of γ′ phase in a ternary phase diagram. The classification of third elements based on the ridge direction does not always agree between ternary Ni 3 Al and NiAl phases.

Thermal conductivity of Ni3X and Pt3X in ordered and disordered states

Abstract Thermal conductivities are measured for a series of Ni 3 X and Pt 3 X compounds in which an ordered L1 2 and f.c.c. disordered structures are formed when the constituent X belongs to the first long period in the periodic table. An empirical rule is found for both ordered and disordered structures that the thermal conductivity tends to decrease as the distance of the constituent X increases in the horizontal direction from the location of Ni and Pt in the periodic table. This trend is quite isomorphic with that of dilute solid solutions of Ni-X or Pt-X, although the magnitude is different. For most Ni 3 X and Pt 3 X compounds, thermal conductivity increases with increasing temperature. The temperature coefficient of thermal conductivity is higher in the disordered compounds than in the ordered compounds.

Thermophysical Properties of Rh 3 X for Ultra-High Temperature Applications

69 Nickel-based superalloys have been the principal high-temperature structural materials for gas turbine engines. Their properties have been improved significantly by alloying additions, directional solidification and by the use of single crystals (1). However, gas turbine engines have developed to the point where their operating temperatures are now close to the melting temperatures of these alloys. A new base material is therefore required if higher material temperatures are to be achieved. Much contemporary research on high-temperature structural materials is centred on intermetallic compounds. Several reviews have addressed the potential for intermetallic alloys (2–7). Among intermetallics, rhodium-based L12 compounds offer advantages for high-temperature structural applications. First, the melting points are 300 to 700 K higher than those of nickel-based superalloys (8). Secondly, the L12 crystal structure offers the possibility of enhanced ductility and excellent workability as a result of the large number of possible slip systems. Finally, the two-phase γ/γ′-type microstructure formed in nickel-based superalloys can also be produced in rhodium-based alloys (9–11). A preliminary study on the mechanical properties of the L12 intermetallic compounds Rh3X (X = Ti, Nb, Ta) is reported elsewhere (12). Rh3Ti shows good ductility up to 30% in compression, over a wide temperature range from room temperature to 1673 K, and both Rh3Nb and Rh3Ta show a positive temperature dependence of strength (a stress anomaly) at around 1273 K. However, by contrast with pioneering work on the mechanical properties of the rhodium-based L12 compounds, few studies on the physical properties of these compounds are found in the literature. Key parameters for the design of high heat-flux alloy structures for high-temperature service include thermal conductivity and thermal expansion (13, 14). Thermal conductivity data are required to determine the feasibility and the basic DOI: 10.1595/147106706X106182